Stateful component

[albinotonnina]

Fixes #13
Can be used like this:

// .babelrc
{
  "plugins": [
    ["inline-react-svg", {
      "statefulComponent": true
    }]
  ]
}

// React
import React from 'react';
import CloseSVG from './close.svg';

const MyComponent = () => <CloseSvg svgRef={el => this.myEl = el} />;

[ljharb]

This will need a rebase.